The Great Master Plan is to move the recognition of special cases for
comparisons further down the compilation pipeline where more information is
available. This is a first step into this direction: The special handling of
equality comparisons involving null is pushed from the parser to the code
generators, removing the need for a special AST node. (There are rumors from
usually well-informed sources that this node type is actually a relic of ancient
crankshaft days...)

The next steps will be the unification of null/undefined handling and pushing
the special case handling in crankshaft even further down the pipeline, enabling
the recognition of cases like "var foo=null; if (foo === bar) ...", but these
will be in separate CLs.
Review URL: http://codereview.chromium.org/7887037

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9293 ce2b1a6d-e550-0410-aec6-3dcde31c8c00